Many metals receive a coating as a way of increasing their functionality. For example, galvanization is the process of coating steel or iron with a zinc coating, which aids in protecting the substrate metal. This process provides the underlying metal with a protective, corrosion resistant layer of zinc. Galvanization may be performed by electroplating. (electrogalvanization) or hot-dipping with the option for heat treating the coating after deposition.
Scrap coated metals are currently a lower value scrap. This is because the coating may interfere with recycling processes or may be emitted as a toxic or hazardous substance. For example, furnaces that process scrap galvanized metal may emit zinc in the flue gas. Some of this zinc bearing waste may be recycled but generally only to mitigate waste disposal costs. The United States Environmental Protection Agency (USEPA) regulates the levels of elements that follow zinc, such as cadmium, in emissions and discharges.
To avoid unnecessary levels of toxic or hazardous emissions, it is sometimes beneficial to remove coatings from metal. In the case of zinc decoating, this can be done through a variety of methods including hydrometallurgical, pyrometallurgical, and mechanical processes.